The family told the Associated Press the singer died of idiopathic pulmonary arterial hypertension, which led to heart failure.

In a statement to the AP, the family said after Cole received a kidney transplant in 2009, she was diagnosed with pulmonary arterial hypertension, a rare lung disease that causes shortness of breath, dizziness and sometimes chest pain. Because Cole's case was idiopathic, the exact cause is unknown.

The statement read: "(Cole) responded well to pulmonary arterial hypertension-specific agents over many years, during which she performed many concerts world-wide, but eventually succumbed to intractable right heart failure, an outcome that unfortunately commonly occurs in this progressive disorder."

Cole died last week at the age of 65. The daughter of Nat King Cole, she became a star in her own right, winning nine Grammys and releasing platinum albums including 1977's Unpredictable and 1991's Unforgettable... with Love. Yet the singer battled early problems with drug abuse, and later hepatitis C. Cole had a kidney transplant in 2009.

"Natalie fought a fierce, courageous battle, dying how she lived ... with dignity, strength and honor. Our beloved Mother and sister will be greatly missed and remain UNFORGETTABLE in our hearts forever," read the statement released last week from her son, Robert Yancy, and sisters, Timolin and Casey Cole.

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Natalie Cole, the unforgettable singer and daughter of the unforgettable singer Nat King Cole, died Dec. 31, 2015. She was 65. Take a look back at pictures from her life. In September 2013, she was interviewed after receiving a Latin Grammy nomination. Chris Pizzello/Invision/AP